General

all the thief classes cept NW, Evan, and Aran

Xenon
Dual Blade
Phantom
Night Lord
Evan

And somewhat Kinesis, to a degree

Kanna and Luminous are also quite popular

xenons! i h8 xenons

Dual Blades and NLs are definitely up there.
You can't have ninja/edgelord classes in a game marketed to young people and not expect tons of them around.

Blaze Wizards are also very very common. Though not for any good reasons. >_>

The most common of all i'd say is Phantoms

@kanji: There will always be those new classes that don't survive the hype. Remember when Kinesis came out? Yeah, I don't either.

You'd think it would be Blasters since they just came out, but nope, I don't see any of those anymore...

I see a TON of Evans, more than a handful of Lumis, lots of Kannas (but mostly mules), and the rest kind of even out, with Explorers a little less often than most.
All in Reboot anyway.

Oh thank god. I thought you were that uhhh player who kept making those classes/damage/bossing/wtf/etc threads
-phew-

To answer your question: I would say the most common classes are Night Lords, Dual Blades, Luminous, Evans, Kaisers and Arans.